A mechanistic study of the photoextrusion of SOb2s to form gbs-lactam rings

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Gargoum, Ali M.
Sousa, Lynn R.
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Thesis (M.S.)--Ball State University, 1983.
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Irradiation of 1,1-dioxo-2-phenyl-4-thiazolidinone resulted in loss of S02 and formation of a carbon-carbon bond. When (2S,5R) cis-3,5-dimethyl-l,l-dioxo-2-phenyl-4thiazolidinone was photolyzed (through a Vycor filter in t-BuOH/CH3CN) (3S,4S) cis-l,3-dimethyl-4-phenyl-2-azetidinone (i.e., optically active cis a-lactam) was obtained as a major product. The synthesis of (2S,5R) cis-3,5-dimethyl1,1-dioxo-2-phenyl-4-thiazolidinone is described. The verification of optical activity was accomplished by the use of Eu(tfc)3.In addition to the earlier data, the above results have helped us to elucidate the mechanistic pathway of S02 photoextrusion to form p-lactam rings. Sensitization experiments by M. R. Johnson and his use of triplet state quencher have shown that the photoextrusion is a singletstate reaction. Johnson's trapping experiments indicated the existence of a radical intermediate. In the work of this thesis, the observation of optical activity of the cis S-lactam product ruled out a planar diradical and a butadiene-like intermediate. Thus, it can be concluded that the S02 photoextrusion process occurs via discrete radical and diradical intermediates. The diradical is probably formed by stepwise loss of S02 and is so shortlived that optical activity along with cis stereochemistry is maintained.Ball State UniversityMuncie, IN 47306